Positioning apparatus employing a magnetized screw thread

ABSTRACT

A positioning apparatus, and method of making same, having two relatively movable members with one of the members having detectable means thereon and the other having reading head means capable of detecting the detectable means whereby such apparatus is capable of precisely relatively moving its members and indicating both the magnitude and direction of movement of one member with respect to the other.

United States Patent Knopf [54] POSITIONING APPARATUS EMPLOYING AMAGNETIZED SCREW THREAD Inventor:

Assignee:

Filed:

Appl. No.:

George S. Knopl, Dayton, Ohio The Bendix Corporation May 13, 1969 US.Cl. ...340/l95, 318/603, 318/568, 318/34 PS, 340/277, 340/205, 235/151.

Int. 1

Field Search ..340/l95, 196,197, 198, 199, 340/271, 282, 347 PR, 174.1;318/568, 603; 235/l51.1, 151.11; 324/34 PS, 34 D, 34 GT AMPLIFIER D. C.LEVEL CONVERTER 3,312,861 4/1967 Mauch Primary Examiner-John W. CaldwellAssistant Examiner-Robert J. Mooney Attorney-Flame, Hartz, Smith &Thompson and Ernest T. Hix

[57] ABSTRACT A positioning apparatus, and method of making same, havingtwo relatively movable members with one of the members having detectablemeans thereon and the other having reading head means capable ofdetecting the detectable means whereby such apparatus is capable ofprecisely relatively moving its members and indicating both themagnitude and direction of movement of one member with respect to theother.

l9Claims,9DrawingFlgures FLIP FLOP INVERTER SUMMING NETWORK MONOS'TABLEMULTIVIBRATOR a) ["1 I04 REVERSIBLE Int/- COUNTER 75/ CONTROL LOGICmmmrsa M972 3.641.535

SHEETlUF3 FIG-l oo oooooo M 77 MS 76A AXIS INVENTOR GEORGE S. KNOPF 5|4| 44 47 7O 23 73 HIS ATTORNEY PATENTEDFEB 81972 SHEET 2 OF 3 5 2 M SNOE Amv XL E r m 4 w E El W 0 mN WK S E 6 R O E G HIS ATTORNEYPOSITIONING APPARATUS EMPLOYING A MAGNETIZED SCREW THREAD BACKGROUND OFTHE INVENTION Many machines in current use, such as machine tools andmeasuring machines, for example, have relatively movable components,such as supports or slides which are movable on associated ways; and itis usually necessary to precisely move a particular support as well asindicate both the magnitude and direction of movement of the supportwith respect to a reference position. In general, present machines use aprecision power actuator to move the support along its ways and aseparate precision measuring device to precisely indicate the movementof such support for control purposes. This duplication of precisioncomponents in a given machine is very expensive and often does notprovide optimum machine performance inasmuch as it is difficult toinstall and maintain such components in the required substantiallyperfect cooperating relationships, especially after extended use of aparticular machine.

SUMMARY This invention provides a precision positioning apparatus, andmethod of making same, wherein such apparatus comprises a pair ofrelatively movable members with one of the members having detectablemeans thereon and the other having reading head means capable ofdetecting the detectable means whereby such apparatus serves a dualpurpose of precisely relatively moving its members and indicating boththe magnitude and direction of movement of one member with respect tothe other.

Other details, uses, and advantages of this invention will becomeapparent as the following description of the exemplary embodimentthereof presented in the accompanying drawings proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show anexemplary embodiment of this invention, in which FIG. 1 is a perspectiveview with pans broken away of an exemplary numerically controlledmeasuring machine which utilizes one exemplary embodiment of theapparatus of this invention;

FIG. 2 is a view, with certain parts shown schematically, illustratingthe exemplary positioning apparatus of this invention utilized with botha vertically movable and a horizontally movable slide assemblycomprising the machine of FIG. I and also generally illustrating byblock diagrams the basic electrical system associated with each slideassembly;

FIG. 3 is an enlarged view of the positioning apparatus for thehorizontal slide of the machine of FIG. 2 which is in the form of athreaded screw and a cooperating threaded nut with certain parts incross section and other parts broken away and also illustrating a pairof reading head means or reading heads comprising such apparatus;

FIG. 4 is a view on the line 4-4 of FIG. 3;

FIG. 5 is a view particularly illustrating the manner in which one ofthe reading heads is offset from an associated detectable means toenable the reading heads to sense the direction of movement of the nutalong its threaded screw,

FIG. 6 is a schematic view showing the nature of the electrical signalsas they enter and exit the electrical system during forward movement ofthe nut and its associated reading heads from a reference position,

FIG. 7 is a view similar to FIG. 6 showing the nature of the electricalsignals during reverse movement;

FIG. 8 is a block diagram particularly illustrating the basic componentsof the electronic system associated with each set of reading heads andutilized to convert the sinusoidal input signals from the reading headsinto pulses which may be readily counted by an electronic countingdevice; and

FIG. 9 is a fragmentary view in elevation illustrating an exemplaryapparatus which may be used to provide detectable LII magnetized markson the-threads of a screw comprising the exemplary positioning apparatusof this invention.

DESCRIPTION OF ILLUSTRATED EMBODIMENT Reference is now made to FIG. 1 ofthe drawings which illustrates an exemplary numerically controlledmeasuring machine 20 which utilizes one exemplary embodiment of theapparatus of this invention. The measuring machine 20 comprises a base21 having an upstanding structural portion 22 at one end thereof andelectrical console 23 which houses the electronic controls for themachine and its components. The

machine 20 has horizontal ways 24 supported on the base 21 and the ways24 support a horizontal slide 25 for reciprocating movement The machine20 also has vertical ways 29 fixed to the upstanding portion 22 whichsupport a carriage assembly 26 for vertical sliding movement and thecarriage assembly carries a substantially horizontally extending arm 27which has a gaging probe 30 suitably supported adjacent its terminalouter end.

The slide 25 and carriage assembly 26 are each moved along theirassociated ways by an exemplary precision positioning apparatus of thisinvention and each apparatus will be designated generally by thereference numeral 31. Only the positioning apparatus 31 comprising theX-axis drive system, i.e., used to move the slide 25, will be describedin detail and it will be appreciated that such description is alsoapplicable to the apparatus 31 comprising the Y-axis drive system andused to move the carriage assembly 26 vertically.

The slide 25 carries a worktable 32 which in turn supports a fixture 33and the fixture 33 may be initially positioned on the worktable 32 by amanually operated adjustment device 34. The fixture 33 has workpiece 35suitably fixed thereto and the workpiece 35 may be preciselyhorizontally positioned with respect to the gage head 30 by theadjustment device 34 so that a gaging probe 36 comprising the gage head30 maybe brought into gaging association with the workpiece 35 toprovide an indication on a visual indicator 37 on the console 23.

Once a workpiece 35 has been properly set up on the machine 20 thegaging probe 36 is brought and maintained in gaging association with theworkpiece 35 by automatic movement of the carriage assembly 26 and slide25 which is controlled by tape command from a tape head 38, see FIG. 2.The movement of carriage assembly 26 and slide 25 is achieved utilizingits associated positioning apparatus 31. If desired, the fixture 33 mayalso have a rotary table as an integral part thereof and after precisepositioning of the gaging probe 36 both vertically and horizontally theworkpiece 35 may be rotated by such rotary table to provide ameasurement of the entire outer periphery of the workpiece 35.

As seen particularly in FIGS. 2 and 3 the movable support or slide 25has a bracket 41 suitably fixed thereto which enables the slide 25 to bemoved by the positioning apparatus 31. The apparatus 31 comprises adriven member 42 which in this example is shown as a threaded nut 42 anda driving member or screw 43 which operatively associates with the lnut42 to move such nut and slide 25 with great precision and in a mannernow to be described.

The screw 43 is supported for substantially frictionless rotation withone end 45 thereof arranged at a fixed position shown at 44 on themachine 20. The screw 43 has its end 45 directly coupled to a drivemotor 46 which is supported on a .fixed support 47 on the machine 20.The opposite end of the screw 43 comprises a plain shaft portion 50which is received in an antifriction bearing assembly 51 carried by asupport 52 which is fixed to a structural portion of the machine 20. Thescrew 43 is precisely held against axial movement by the motor 46 andcooperating bearing assembly 51 yet is easily rotated either clockwiseor counterclockwise by such motor.

The nut 42 is threaded on the screw 43 and fixed to the bracket 41 andsuch bracket has a comparatively large opening therein so as to allowthe screw 43 to pass therethrough in an unobstructed manner. Uponrotating the screw 43 in one direction the net effect is to move thedriven nut 42 along the driving screw 43 in a corresponding directionand upon rotating the screw 43 in the opposite direction it will be seenthat the nut 42 and slide 25 are moved in a corresponding oppositedirection. In this example, the screw 43 is shown provided withconventional left-hand threads and the nut 42 has a cooperating threadedopening extending therethrough whereby clockwise rotation of the screw43, as viewed looking from the motor 46 toward the gage head 30, resultsin what will be referred to in this specification as forward movement ofthe slide 25, i.e., forwardly from motor 46 toward gage head 30; andcounterclockwise rotation of the screw 43 results in reverse movement ofsuch slide.

The exemplary threaded screw 43 is comprised of ferrous material and hasdetectable means thereon, which will be described in more detailsubsequently, and the nut 42 has cooperating head means comprised of apair of reading heads 54 and 55. The reading heads 54 and 55 operativelyassociate with the detectable means during movement of the nut 42relative to the screw 43 and precisely determine any relative movementtherebetween. In this example of the invention the reference to relativemovement refers to the position of the nut 42 as it is threaded alongthe drive screw 43 and for convenience may be considered as the axialmovement of the nut 42 along the screw 43 from its end 45 whichcoincides with the fixed reference position 44.

The reading heads 54 and 55 operatively associate with the detectablemeans on the screw 43 and determine not only the magnitude of themovement of the nut 42 and hence slide 25 from the reference position 44but also the direction of movement of such nut 42 from the referenceposition 44 in a manner which .will be described in detail subsequentlytogether with the exemplary electrical system which operates inassociation with the reading heads 54 and 55.

The screw 43 may be of conventional construction and comprises aplurality of threads 56 each having a substantially flat crest. Eachthread 56 has the previously mentioned detectable means provided thereonand in this example of the invention such detectable means is in theform of a plurality of spaced magnetized marks which for convenience andease of presentation have been indicated by lines 57, see FIGS. 3 andhowever, it will be appreciated that such magnetized marks would inreality be magnetized regions or areas which are invisible to the nakedeye. The reading heads 54 and 55 are in the form of magnetic readingheads and the magnetized marks 57 are of such a character that they arereadily detected by the reading heads 54 and 55.

The driven member or nut 42 is preferably a split nut having a pair ofcooperating portions 61 and 62 which are suitably fixed together in aknown manner with appropriate spacers or shims so that each portion 61or 62 is urged against one surface of an associated thread while theother portion is urged against an oppositely arranged surface of anassociated thread. With this construction the nut 42 may be moved inboth directions along the threaded screw 43 and there will be no lostmotion upon reversing the direction of movement. To minimize frictionaldrag and assure a smooth operation the nut 42 may be in the form of aball nut, which utilizes recirculating ball bearings which arerecirculated in a known manner by external tubes 63, and the nut 42 hasits portion 62 suitably fixed to the bracket 41.

The head means 54 and 55 of this example comprise magnetic readingheads; and it will be appreciated that such heads may be of theread-write variety, with each head having a portion capable of applying,i.e., writing the magnetized marks 57 against the crest of each thread56, as well as reading or detecting such marks 57.

The reading heads 54 and 55 are fastened to supports 64 and 65respectively and the supports 64 and 65 are attached to nut portion 61of nut 42. The reading heads may be adjustably fastened on theirassociated supports 64 and 65 and suitable means are providedon thesesupports and nut portion 61 to enable supports 64 and 65 to be angularlypositioned relative to each other and thereby assure the reading headsare accurately positioned relative to the magnetized marks 57 to provideelectrical output signals having a sine-cosine relationship for reasonswhich will be apparent later in this disclosure. Although the readingheads 54 and 55 of this example are in essence supported by the nutportion 6], it will be appreciated that such reading heads may besupported in any desired manner by the nut 42.

Each thread 56 has a flat crest portion as previously mentioned and themagnetized marks 57 are provided on the flat crest at spaced intervals.and arranged so that they may be readily detected by the reading heads54 and 55. However, the threads 56 may be of any suitable constructionand need not necessarily have flat crests, provided that the magnetizedmarks are provided at locations, preferably adjacent the crest of eachthread, where they may be readily detected by the reading heads.

As seen in FIGS. 2 and 3, the actuating portion of the X-axispositioning apparatus 31 is defined by the screw 43 and nut 42 whichhave a common axis 66 which is arranged horizontally and parallel to themotion of the slide 25. Inasmuch as the reading heads 54 and 55 arefixed to the nut 42 and the magnetized marks 57 are provided on thethreads 56 of the screw 43, it will be seen that the actuating portionand the position indicating portion of apparatus 31 have a common axis66. With this arrangement a significant source of error of the typewhich might otherwise occur in previously proposed devices due tomisalignment of the axes of a slide actuator and a position indicatingdevice is avoided.

The reading heads 54 and 55 are positioned with respect to themagnetized marks 57 so that with one of the reading heads positioneddirectly over a particular mark the other reading head is arranged apredetermined distance between a pair of associated marks. Inparticular, the reading head 54 of this example of the invention ispositioned directly over a mark 57, as indicated at 67, see FIG. 5,while the reading head 55 is positioned approximately one-quarter of thedistance away from the most closely adjacent mark 57 toward the nextmark as indicated at 68.

Each of the reading heads 54 and 55 upon beingbrought into associationwith a magnetized mark 57 will produce an output signal which issubstantially sinusoidal in form as each head is moved along the screw54. The placement of the reading heads 54 and 55 in the mannerillustrated enables the reading head 54 to provide an output in the formof a sine wave while the displacement of the reading head 55 by roughlyas indicated above results in the reading head 55 providing an output inthe form of a cosine wave. This sine-cosine wave relationship enablesthe determination of the direction of movement of the reading heads 54and 55 from the reference position 44. Further, the electrical circuitswhich may be utilized in association with the reading heads 54 and 55 tomodify the signals detected by each reading head 54 and 55 and convertsuch signals to useable electrical pulses capable, of being counted todetermine magnitude and direction of movement will now be described indetail.

The magnetic reading heads 54 and 55 sense the magnetic flux density ofthe magnetized marks 57 and produce an electrical output signal which isproportional to the magnitude, i.e., strength, of such density. Thereading heads 54 and 55 may he flux bridge devices of known constructionwhich detect flux unbalance even though there is no relative movementbetween the threaded screw 43 and nut 42 whereby the heads 54 and 55 donot require movement or a breaking of the magnetic lines of force inorder to provide an output signal therefrom. Because the heads 54 and 55are of kniwn construction a more detailed description of their constrution and operation is considered unnecessary. It will also beappreciated that the magnetic heads 54 and 55 may be of the type whichrequire external excitation, which may be provided in any manner whichis well known in the art, to assure that with the nut 42 and screw 43 ina stationary position useable output signals will be provided from theheads 54 and 55. The

signals from the heads 54 and 55 are provided to an associated X-axiselectronic circuit through lines 70.

Reference is now made to FIGS. 2 and 6 of the drawings, wherein it willbe seen that the arrangement of thereading heads 54 and 55 is such thatwith movement of the nut 42 and slide 25 in a forward direction, i.e.,forwardly from fixed reference position 44 toward the gage head 30, thesinusoidal signal indicated at 71 from the gage head 54 leads the signalindicated at 72 from the gage head 55 by approximately 90 and enters theX-axis electronic circuit shown by a block diagram and designated by thereference numeral 73. The sinusoidal signals are modified and rendereduseable by the electronic circuit or system 73 so that for forwardmovement sharply defined useable pulses are provided which have the formillustrated at 74 in FIG. 6. The pulses 74 are fed to a logic network 75through lines 76 and 77, see FIG. 2, where they are compared withcommand signals from the machine input circuit which in this example ofthe invention comprises an input from the tape head 38. If desired, anoutput may also be provided from the control logic network to a feedbacksystem (not shown) and the output may be utilized in a known manner toenergize the motor 46 and reposition the slide 25 as a function of thecommand signal from the feedback system. The output pulses of the typeindicated at 74 may also be pro vided through lines 76 to a reversibleelectronic counter 78 which is operatively connected to a visualindicating device 79 which may indicate the exact position of the slide25 with respect to the reference position 44, for example, by displayinga corresponding dimensional measurement.

With reverse movement of slide 25 the sinusoidal signal indicated at 80,see FIG. 7, from the gage head 54 lags the signal indicated at 81 fromthe gage head 55 by approximately 90 as it enters the X-axis electroniccircuit 73 where it is modified and rendered useable. For reversemovement sharply defined useable pulses are provided which have the formillustrated at 82. The pulses for reverse movement are also fed to logicnetwork 75 through lines 76 and 77 and to the reversible counter 78through lines 76.

As previously stated, the detailed description is being made for thepositioning apparatus 31 and electronic circuitry associated with thedual-purpose drive and position indicating system for the horizontalslide 25; however, it will be appreciated that substantially identicalcomponents are used with the positioning apparatus 31 associated withthe vertically movable carriage assembly 26. Accordingly the Y-axiselectronic system is also presented as a block diagram and designated bythe reference numeral 73 followed by the letter designation A and willnot be described in detail. Similarly the electrical lines from heads 54and 55 associated with the Y- axis system apparatus 31 to the Y-axiselectronic system and the other electrical components with connectinglines for the Y-axis system will also be designated by the samereference numerals as corresponding members of the X-axis system andeach of such members will also have its reference numeral followed bythe letter designation A and not described again.

Reference is now made to FIG. 8 of the drawings for a more detailedpresentation of the component portions of the X-axis electronic systemwhich is associated with the positioning apparatus 31 for the horizontalslide 25. The presentation in FIG. 8 has been made using block diagramsand the waveforms of the electrical signals exiting each major componentof the system have also been illustrated for ease of understanding. Thedetailed electrical parts comprising each major component shown in FIG.8 may be of any suitable known construction and hence the presentationis considered fully adequate to enable one skilled in the art to providean operating system from the information presented.

Also, for ease of presentation different reference numerals have beenused to indicate the different waveforms of the signals exiting eachmajor component and each reference numeral may be used interchangeablyto refer to either the waveform or the electrical signal. The waveformsof the signals are presented by solid lines and are for forward movementof the slide 25. A few signals have been presented by dotted lines andthe dotted waveforms are for reverse movement of the slide.

The signal from the magnetic reading head 54 is indicated at 71 and isshown leading, by 90, the signal from the reading head 55 indicated at72. The signals are amplified in an amplifier 85 and the amplifiedsignals from the reading heads 54 and 55 have waveforms as illustratedat 86 and 87 respectively. The signals from the amplifier 85 aresupplied to a DC level converter 90 so that the waveforms 86 and 87 areconverted to amplified waveforms as shown at 91 and 92 respectively.

The signals indicated at 91 and 92 are then fed to a multivibrator orflip-flop 93. The flip-flop 93 is in essence a squaring device used toobtain square waves from the roughly sinusoidal signals from the DClevel converter 90 whereby the signals exiting the flip-flop 93 havewaveforms as illustrated at 94 and 95. The signals 94 and 95 aresupplied to an inverter 96 which provides a pair of counterphase signalshaving waveforms 97 and 98 respectively.

The signals 97 and 98 are then supplied to a summing network 100 whichis comprised of two identical channels 101 and 102 with channel 101having only the forward count pulses exiting therefrom and channel 102having only the reverse count pulses exiting therefrom. Each channel 101and 102 has sets of diodes 103 and 104 associating respectivelytherewith and each set of diodes allows only a negative signal to passtherethrough.

The waveforms of the signals from the summing network 101 during forwardmovement of the slide 25 are shown at 105 and 106 with the signal fromthe reading head 54 leading. The signals 105 and 106, during forwardmovement, are supplied to a monostable multivibrator 110 so that thesignals exiting the multivibrator 1 10 have waveforms as indicated at111 and 112 whereby the signal 112 is not useable and the signal 111 isa distinct useable signal which may be supplied to the control logicnetwork 75 and to the counter 78 (as forward count pulses) utilizing anassociated one of the lines 76.

During reverse movement of the slide 25 the signal through the reversechannel 102 will be such that once the modifiedsignal from the readinghead 55 exits the summing network 100 it has a waveform as indicated at114 while the modified signal from reading head 54 has a waveform asindicated at 115. The signals 114 and 115, during reverse movement, aresupplied to the multivibrator 110 so that the signals exiting suchmultivibrator have waveforms as indicated at 116 and 117 respectivelywhereby the signal 117 is not useable and the signal 116 is a distinctuseable signal which may be supplied to the control logic network 75 andto the counter 78 (as reverse count pulses) using the other of the lines76.

Thus, the diodes at 103 and 104 operate to block passage of any positivevoltages and allow only negative voltages, i.e., signals, to'passthrough to the monostable multivibrator 110 arranged downstream thereof.Further, during forward movement of the slide 25 only forward pulses 111exit the multivibrator 110 and during reverse movement only reversepulses 116 exit multivibrator 110.

Thus, it is seen that the apparatus 31 of this invention provides apower-actuating device capable of precisely moving an associated memberthereof such as nut 42, with slide 25 fixed thereto, along a precisionscrew 43 and the apparatus 31 has an electrical circuit capable ofprecisely determining both the magnitude and direction of movement ofthe slide 25 with respect to a reference position 44 by providingassociated reading heads which have sinusoidal outputs and a sine-cosinerelationship. 1

The nut 42 and screw 43 may be of any suitable conventional constructionas previously mentioned and may be made on conventional machines.Further, manufacturing costs can be kept at a minimum, while stillproviding a precision apparatus, because of the unique apparatus andmethod used to apply detectable means such as magnetized marks on thescrew 43.

Following the manufacture of the screw 43 and the nut 42 these membersmay be suitably operatively associated by threading the nut along thescrew 43 and th; nut 42 may be suitably preloaded by relatively movingits portions 61 and 62 and fixing such portions in position to eliminateany backlash due to reversing the rotation of the nut 42 along the screw43. The assembled screw 43 and nut 42 may then be placed in position onany associated fixture 118, see FIG, 9.

In particular the nut 42 may be fixed to a slide 119 which is supportedfor precise rectilinear movement along horizontal ways 120. A suitablehead means, shown as head 54in this example inasmuch as such head is aread-write head, is attached firmly to the nut 42 and positioned so thatit will place detectable means in the form of magnetized marks 57 on theperiphery of the screw 43 upon command from an associated control 122.The nut 42 is placed in threaded engagement at one end of the screw 43and an independent measuring device 123 is placed in operativeassociation with the nut 42 as shown at 124.

The screw 43 is supported by a bearing assembly 125 at one end and by adirectly coupled motor 126 at its other end whereby it is confinedagainst axial movement. The screw 43 is rotated by the motor 126 causingaxial movement of the nut 42 therealong and at predetermined axialpositions of the nut 42 along the screw 43, as determined by themeasuring device 123, the control 122 is energized causing it toenergize the head 54 and place a corresponding magnetic mark 57 on thatportion of an associated thread 56 aligned beneath the head 54.

Following the complete traverse of the nut 42 from one end of the screw43 to the other a complete spiral track of magnetized marks 57 will beprovided on the screw 43 and the pulses may be precisely spaced so thatthe separation between each immediately adjacent pair of magnetizedmarks will be equivalent to a fixed linear movement of the nut 42 alongthe axis of the screw 43. This technique may result in a nonuniformplacement of magnetized marks 57 on the periphery of the screw but wouldclearly result in a proper spacing of the magnetized marks if consideredonly relative to motion in an axial direction.

Should the screw and nut combination be subsequently tested and it isfound that the placement of magnetized marks 57 does not provide thedesired accuracy, these marks could be easily magnetically erased, inthis example, and the lead screw 43 returned to the associatedcalibration fixture 118 and a new set of magnetized marks recordedthereon.

In this example of the invention the long-range measuring device 123 isshown schematically as an optical grating system which uses reflectivegratings, including an elongated fixed scale grating; a movablecomparatively short index grating; and the required associatedcomponents including a light source, photoelectric cells, collimatinglens, etc. Because such a measuring device is well known in the art itwill not be described in more detail. It will also be appreciated thatother suitable long-range measuring devices may be used with the fixture118, such as a laser interferometer, for example.

In some applications of this invention it may be preferred to mount thescrew 43 and nut 42 in position on an associated machine such as themachine 20. A separate measuring device, such as the device 123, maythen be installed in position and operatively associated with one end ofthe nut 42 so that upon rotating the screw 43 the nut is moved axiallyalong such screw and magnetized marks 57 may be placed on the screw 43using the read-write head 54 for example. With this technique any errorsmade in manufacturing a particular combination of screw and nut areautomatically compensated for. In addition, errors made in installingthe screw and nut and associated components on a particular machine arealso compensated for.

' The long track defined by the spiral path of the threads on the screw43 provides a comparatively long linear track on which to applymagnetized marks for a given axial distance that the nut 42 travelsalong the screw 43. This obviously reduces the accuracy with which themagnetized marks must be placed on the screw 43 and thereby increasesthe overall accuracy of. the system. Also, if the state of the artlimits grating lines of an optical system to a thousand lines per inchthe overall system accuracy is limited accordingly. However, by using ascrew 43 having a 3-inch diameter, for example, and four threads perinch, approximately 40,000 lines could be recorded per inch of axialmovement. Obviously, this offers substantial improvement overresolutions offered by currently available devices similar in functionto the apparatus 31.

The above description may suggest that the application of magnetizedmarks requires intermittent movement of the nut 42 along the screw 43and the placement of a magnetized mark by the writing head portion ofthe head 54 on the screw 43 while the head is stopped. However, it willbe appreciated that the screw 43 may be continuously rotated therebymoving the nut 42 therealong whereby magnetized marks 57 could bereadily applied during continuous movement of the nut 42 along the screw43.

In this example of the invention the reading heads 54 and 55 are shownas magnetic reading heads and the detectable means are shown asmagnetized marks 57. However, it will be appreciated that the concept ofproviding a power actuator and a position indicator as one integral unitmay be utilized not only where the detectable means comprises magneticmarks 57 and the heads comprise magnetic reading heads similar to 54 and55 but also where the marks may be purely mechanical and defined asscribed lines or photographic lines generated by a light beam impingingon a photographic emulsion on the lead screw, for example. Likewise theassociated reading heads may be electrooptical reading heads whichprovide sinusoidal output signals similar to the signals described indetail in connection with the magnetic reading heads 54 and 55.

v In this example of the invention only a pair of reading heads 54 and55 have been illustrated; however, it will be appreciated that eachreading head 54 and 55 may be of the type which operatively associateswith a plurality of magnetized marks 57 and emits an average sinusoidaloutput signal therefrom which may be amplified and placed in suitableform for further use in a similar manner as previously described. Inaddition, the reading heads 54 and 55 instead of being spaced from thescrew 43 as shown may, if desired, be of the type which slidably contactsuch screw during movement of the nut 42 therealong.

In utilizing a positioning apparatus which employs a magnetic system itis. also entirely within the scope of this invention to providemagnetized marks 57 on the screw 43, each having clearly discerniblenorth and south poles whereby a single-reading head may be utilized todetect not only the magnitude of movement of a nut42 from a referenceposition 44 but also the direction of such movement from the referenceposition.

The actuating system of this example is shown as being defined by athreaded screw 43 and a cooperating ball nut 42. However, it will beappreciated that the concept of this invention is fully applicable toother types of actuators whether they be linear actuators, rotaryactuators, or combinations of such, and such actuators may be powered bymechanical, electrical, or fluid means. However, regardless of its typeeach particular actuator enables precision power actuation as well asprecision indication of position from a reference position. In addition,any suitable electronic means may be provided to reset the reference orzero position to any point along the screw 43 and provide a precisionindication of position in either direction from such point. 1

Each magnetized mark 57 has been described as producing a signal whichis picked up by an associated reading head and subsequently utilized inthe manner described above. However, it will be appreciated that throughknown electronic techniques means may be provided for producing signalsintermediate each immediately adjacent pair of magnetized marks 57 tothereby provide interpolation between marks and hence a more preciseindication of position.

While present exemplary embodiments of this invention, and methods ofpracticing the same, have been illustrated and described, it will berecognized that this invention may be otherwise variously embodied andpracticed by those skilled in the art.

What is claimed is:

1. An apparatus for relatively moving two members and preciselydetermining the relative movement therebetween, said apparatuscomprising, a driven member and a driving member operatively associatingwith said driven member to move said driven member, one of said membershaving detectable means thereon and the other of said members havingcooperating head means, said head means precisely determining saidrelative movement by operatively associating with said detectable meansduring movement of said driven means by said driving means.

2. An apparatus as set forth in claim 1 in which one of said members issupported on a structural portion of a machine and the other of saidmembers comprises a part of a movable support comprising said machine.

3. An apparatus as set forth in claim 1 in which said head meansprovides electricalsignals during said operative association which areutilized to determine both the magnitude of said relative movement andthe direction of movement of one of said members from a referenceposition.

4. An apparatus as set forth in claim 1 in which, one of said members issupported on a structural portion of a machine, the other of saidmembers comprises a part of a movable support comprising said machine,and said head means comprises at least two reading heads arranged inspaced relation and each providing a sinusoidal electrical signaltherefrom during said operative association, one of said reading headsproviding substantially a sine signal the other of said reading headsproviding substantially a cosine signal, said signals being utilized todetermine both the magnitude of said relative movement and the directionof movement of said other member and its associated movable support froma reference position.

5. An apparatus as set forth in claim 1 in which said driven membercomprises a threaded nut assembly and said driving member comprises acooperating threaded screw.

6. An apparatus as set forth in claim 1 in which said head meanscomprises at least one read-write head.

7. An apparatus as set forth in claim 1 in which said detectable meanscomprises a plurality of spaced magnetized marks and said head meanscomprises at least one read-write magnetic head capable of applying saidmagnetized marks at predetermined spaced intervals as well as preciselydetecting each of said marks.

8. An apparatus as set forth in claim 1 in which said members have acommon axis, said driving member drives said driven member along saidcommon axis, and said head means determines said relative movement alongsaid common axis enabling said head means to determine said relativemovement with optimum precision.

9. An apparatus as set forth in claim 1 in which, said one membercomprises a threaded screw supported for reversible rotation with oneend thereof coinciding with a fixed reference position of a machine,said other member comprises a cooperating threaded nut assembly fixed tosupport of said machine which is adapted to be moved in a reciprocatingmanner on said machine by said screw, and said head means being utilizedto determine both the magnitude of said relative movement and thedirection of movement of said support with respect to said referenceposition.

10. An apparatus as set forth in claim 9 in which said detectable meanscomprises a plurality of marks on each thread adjacent the crest thereofand said head means comprises a plurality of cooperating reading heads.

11. An apparatus as set forth in claim 9 in which said nut comprises asubstantially frictionless ball nut capable of being preloaded againstopposed surfaces of adjacent threads of said screw to prevent lostmotion during change of direction of rotation of saidscrew.

12. In combination: a machine having a movable support and adual-purpose apparatus for moving said support on said machine andprecisely determining the movement of said support from a referenceposition, said apparatus comprising, a driven member, a driving memberoperatively associating with said driven member to move said drivenmember, one of said members being supported adjacent said referenceposition and the other of said members being carried by said support,detectable means on one of said members, and cooperating head meanscarried by the other of said members, said head means preciselydetermining both the magnitude and direction of said movement from saidreference position by operatively associating with said detectable meansduring movement of said driven means by said driving means.

13. A combination as set forth in claim 12 in which said head meansprovides electrical signals during said operative association which areutilized in determining said movement.

14. A combination as set forth in claim 12 in which said head meanscomprises a read-write head adapted to apply said detectable means onsaid one member with said members installed in operative association onsaid machine whereby inherent errors made in manufacturing andassembling said members and their associated components areautomatically compensated for during the application of said detectablemeans.

15. A combination as set forth in claim 1 in which said detectable meanscomprises a plurality of spaced magnetized marks and said head meanscomprises a pair of cooperating magnetic reading heads.

16. A combination as set forth in claim 12 in which said driven membercomprises a threaded nut assembly and said driving member comprises acooperating threaded screw.

17. A combination as set forth in claim 16 in which said head meanscomprises at least two reading heads arranged in angularly spacedrelation about the periphery of said nut, each of said reading headsproviding a sinusoidal electrical signal therefrom during said operativeassociation, one of said reading heads providing substantially a sinesignal and another of said reading heads providing substantially acosine signal, and said signals being used to determine said magnitudeand direction of movement from said reference position.

18. A combination as set forth in claim 12 in which said machine hasways for supporting said support, said support comprises a slide, saiddriven member comprises a substantially frictionless threaded ball nutfixed to said support, and said driving member comprises a cooperatingthreaded screw supported on said machine for reversible rotation withone end thereof coinciding with said reference position.

19. A combination as set forth in claim 18 and further comprising areversible motor directly coupled to one end of said screw to providesaid reversible rotation with optimum efficiency.

1. An apparatus for relatively moving two members and preciselydetermining the relative movement therebetween, said apparatuscomprising, a driven member and a driving member operatively associatingwith said driven member to move said driven member, one of said membershaving detectable means thereon and the other of said members havingcooperating head means, said head means precisely determining saidrelative movement by operatively associating with said detectable meansduring movement of said driven means by said driving means.
 2. Anapparatus as set forth in claim 1 in which one of said members issupported on a structural portion of a machine and the other of saidmembers comprises a part of a movable support comprising said machine.3. An apparatus as set forth in claim 1 in which said head meansprovides electrical signals during said operative association which areutilized to determine both the magnitude of said relative movement andthe direction of movement of one of said members from a referenceposition.
 4. An apparatus as set forth in claim 1 in which, one of saidmembers is supported on a structural portion of a machine, the other ofsaid members comprises a part of a movable support comprising saidmachine, and said head means comprises at least two reading headsarranged in spaced relation and each providing a sinusoidal electricalsignal therefrom during said operative association, one of said readingheads providing substantially a sine signal the other of said readingheads providing substantially a cosine sIgnal, said signals beingutilized to determine both the magnitude of said relative movement andthe direction of movement of said other member and its associatedmovable support from a reference position.
 5. An apparatus as set forthin claim 1 in which said driven member comprises a threaded nut assemblyand said driving member comprises a cooperating threaded screw.
 6. Anapparatus as set forth in claim 1 in which said head means comprises atleast one read-write head.
 7. An apparatus as set forth in claim 1 inwhich said detectable means comprises a plurality of spaced magnetizedmarks and said head means comprises at least one read-write magnetichead capable of applying said magnetized marks at predetermined spacedintervals as well as precisely detecting each of said marks.
 8. Anapparatus as set forth in claim 1 in which said members have a commonaxis, said driving member drives said driven member along said commonaxis, and said head means determines said relative movement along saidcommon axis enabling said head means to determine said relative movementwith optimum precision.
 9. An apparatus as set forth in claim 1 inwhich, said one member comprises a threaded screw supported forreversible rotation with one end thereof coinciding with a fixedreference position of a machine, said other member comprises acooperating threaded nut assembly fixed to a support of said machinewhich is adapted to be moved in a reciprocating manner on said machineby said screw, and said head means being utilized to determine both themagnitude of said relative movement and the direction of movement ofsaid support with respect to said reference position.
 10. An apparatusas set forth in claim 9 in which said detectable means comprises aplurality of marks on each thread adjacent the crest thereof and saidhead means comprises a plurality of cooperating reading heads.
 11. Anapparatus as set forth in claim 9 in which said nut comprises asubstantially frictionless ball nut capable of being preloaded againstopposed surfaces of adjacent threads of said screw to prevent lostmotion during change of direction of rotation of said screw.
 12. Incombination: a machine having a movable support and a dual-purposeapparatus for moving said support on said machine and preciselydetermining the movement of said support from a reference position, saidapparatus comprising, a driven member, a driving member operativelyassociating with said driven member to move said driven member, one ofsaid members being supported adjacent said reference position and theother of said members being carried by said support, detectable means onone of said members, and cooperating head means carried by the other ofsaid members, said head means precisely determining both the magnitudeand direction of said movement from said reference position byoperatively associating with said detectable means during movement ofsaid driven means by said driving means.
 13. A combination as set forthin claim 12 in which said head means provides electrical signals duringsaid operative association which are utilized in determining saidmovement.
 14. A combination as set forth in claim 12 in which said headmeans comprises a read-write head adapted to apply said detectable meanson said one member with said members installed in operative associationon said machine whereby inherent errors made in manufacturing andassembling said members and their associated components areautomatically compensated for during the application of said detectablemeans.
 15. A combination as set forth in claim 1 in which saiddetectable means comprises a plurality of spaced magnetized marks andsaid head means comprises a pair of cooperating magnetic reading heads.16. A combination as set forth in claim 12 in which said driven membercomprises a threaded nut assembly and said driving member comprises acooperating threaded screw.
 17. A combination as set forth in claim 16in which said head means comprises at least two reading heads arrangedin angularly spaced relation about the periphery of said nut, each ofsaid reading heads providing a sinusoidal electrical signal therefromduring said operative association, one of said reading heads providingsubstantially a sine signal and another of said reading heads providingsubstantially a cosine signal, and said signals being used to determinesaid magnitude and direction of movement from said reference position.18. A combination as set forth in claim 12 in which said machine hasways for supporting said support, said support comprises a slide, saiddriven member comprises a substantially frictionless threaded ball nutfixed to said support, and said driving member comprises a cooperatingthreaded screw supported on said machine for reversible rotation withone end thereof coinciding with said reference position.
 19. Acombination as set forth in claim 18 and further comprising a reversiblemotor directly coupled to one end of said screw to provide saidreversible rotation with optimum efficiency.